Pour one out for Uraha. o7
In case it wasn't explicit to some, everything pertaining to Uraha was a biblical reference.
Caina is a female version of
Cain, the first son of Adam and Eve who was punished by God, hence she is depicted as a fallen angel. She is also obviously trying to bring about a flood like in the Book of Genesis.
Michael is based on the
archangel Michael, guardian of Irsael. This reference is a bit clearer in Japanese since you can see the pronunciation of the name is the Hebrew one rather than the English one (so like Mikhail).
Michael's true identity, Avel, is also a female version of
Abel, the second son of Adam and Eve, and who God favored over Cain.
This conflict also serves as a parallel to how Cain is depicted as the originator of evil whereas Abel is depicted positively, being the first ever murder victim at the hands of Cain, except here the roles are reversed.
In any case, 14 chapters to go! Almost there!